The auditory system, like other sensory systems, is constructed of multiple neuronal pathways, each carrying information from the periphery to the forebrain via distinct sets of neurons and each with its own role to play in the overall function of the system. The auditory system has the advantage, as a system for anatomical, physiological, biochemical, and behavioral studies, that many of the neurons that participate in particular pathways are not only morphologically distinguishable but also spatially segregated from the neurons in other pathways. The goal of this research is to discover principles of synaptic organization and of topographic projection patterns that form the morphological basis for stimulus coding by neurons in the auditory system. The specific aims can be summarized as follows: 1) To understand the structural basis for binaural processing in the cochlear nucleus and the superior olivary complex by identifying and describing the synaptic organization of the neurons involved; 2) To elucidate the role of the small cell cap of the ventral cochlear nucleus in the processing of auditory information by describing its connections with cells in the cochlea and other parts of the auditory system; and 3) To determine the topography of the projections from specific neuronal types in the ventral cochlear nucleus to the superior olivary complex and inferior colliculus. Methodology used to achieve these aims will include electron microscopy of both normal and experimental material and neuroanatomical tracing techniques based on axonal transport. In humans, normal inputs over the auditory pathways, especially during early life, appear to be important for the realization of normal intellectual potential and the ability to comprehend and produce normal speech. Abnormalities in specific parts of the multiple auditory pathways, although they may not produce absolute deafness, may thus result in profound abnormalities in the central nervous system. Understanding of the normal structure of the system in terms of the organization of each of the multiple pathways that ascend from the periphery to cortical levels will allow the development of models of auditory function that will, in turn, allow the formulation of questions about the mechanisms of abnormal function.